The handling of substantially tubular and very long objects is a difficult operation, particularly when the object handled has a flexible and brittle structure comprising, for example, a succession of relatively brittle objects placed in a more flexible tubular sheath, or even when the object exhibits irregularities of diameter over its length. The problem arises in particular in the case of the sonar systems, which surface vessels or submarine vessels are equipped with. The effectiveness of the detection of these systems is greatly dependent on the length of the antenna, and very long tubular antennas, for example of flute type, are generally used. As is known, such linear antennas have a length of several hundred meters for a diameter of the order of a few centimeters. In a mission, the antenna has to be put to sea, deployed to a sufficient length, then raised back on board the vessel at the end of the mission. This operation is difficult, both in the case of a surface vessel, likely to be exposed to a choppy sea, and in the case of a submarine vessel for which the antenna and the towing device are submerged.
Various towing devices have attempted to resolve these difficulties. There is known, for example from the patent published under the reference U.S. Pat. No. 5,839,636, a device of caterpillar type ensuring the towing of the antenna by means of two tracks facing one another and in contact with the antenna to be displaced. Also known from the applicant is the towing device described in the patent application published under the reference FR 2858309. The principle of this known device is recalled hereinbelow by means of FIG. 1. The general idea of the device is to decouple the loads exerted on the object to be towed by separating means continuously ensuring the gripping of the object and means ensuring the pulling of the object.
As illustrated in FIG. 1, such a towing device comprises a frame 11 supporting the following two means:                Pulling means, mainly consisting of two treads 12 arranged on either side of and along the object to be towed 10. Each tread 12 is wound around two pulleys 13 and 14 fixed onto uprights situated at each of the ends of the main frame.        Gripping means, consisting of a first flange 15 and of a second flange 16, in the form of disks, linked to one another by uprights 19. The flanges 15 and 16 are mounted to be rotationally mobile about the longitudinal axis of the device referenced X, by means of holding parts 17 and 18 via bearings for example. The assembly forms a frame 114 that is rotationally mobile relative to the frame 11. The central parts of the flanges 15 and 16 and of the holding parts 17 and 18 are holed, so as to be able to be passed through by the object 10 to be towed and the treads 12.        
The gripping means ensure the contact between the treads 12 and the object to be towed 10 by means of a belt 110 helically wound around the object to be towed and portions of the treads in contact with the object. The winding is sufficiently tight to keep the object and the treads in close contact. The ends of the belt are connected together to form a straight strand 111 which runs in the grooves of the opposing pulleys 112 and 113, fixed respectively onto each of the flanges 15 and 16. The function of these pulleys 112, 113 is notably to ensure the tension of the belts fixed respectively to each of the flanges 15, 16. The assembly consisting of the flanges 15 and 16 and of the uprights 19 forms a frame 114 that is rotationally mobile about the longitudinal axis of the device.
To perform the towing of the object 10, the device also comprises means setting the pulling and gripping means in motion. These means comprise a main shaft 115 and a system of gears and of gearboxes 116 to which secondary shafts are coupled making it possible to rotate the pulleys 14 which ensure the driving of the treads 12, and the pulley 16 which drives the frame 114 in rotation. In the exemplary embodiment, the pulley 16 is coupled via a belt 122 to another pulley 121 secured to the shaft 115.
To ensure the displacement of the object 10 in the direction indicated by the arrow 118, the shaft 115 is actuated by means of a flywheel 117 so that the rotation of the pulleys 14 drives the displacement of the treads 12 in the direction indicated by the arrows 119. The displacement of the treads drives an identical displacement of the object 10. At the same time, the rotation of the shaft 115 rotates the frame 114 in the direction indicated by the arrow 120. This rotation drives the winding of the belts 110 on the side of the flange 15 and a simultaneous unwinding on the side of the flange 16. The effect of this dual action is to provoke a relative displacement of the gripping means along the object 10, in a direction opposite to the real displacement of the object 10 and of the treads 12. Thus, the object 10 is able to progress linearly while being kept closely in contact with the treads. The displacement movement of the object is similar to the linear and continuous displacement of the free jaws of a vice along the worm screw which is used to tighten it, when the vice is tightened or untightened. Conversely, since the operation of the device is symmetrical by construction, the displacement of the object 10 in the opposite direction will be able to be ensured by maneuvering the shaft 115 in the opposite direction by means of the flywheel 117. For the towing action to be effectively feasible, the rotational movement of the frame drives a relative displacement substantially equal to the displacement imparted on the object by the rotation of the treads 12. The coordination of the two movements can be ensured by mechanical means, for example a gearbox device mounted on the shaft 115.
This device presents many advantages compared to the prior devices, for example of caterpillar type. In particular, the separation of the gripping and pulling functions into two means makes it possible to decouple the two loads exerted on the object, making it possible to exert an effective pulling force, without having to exert an excessive, and even damaging pressure on the object to be towed. Difficulties have however been observed that the present invention seeks to resolve.
The belt of the gripping means is a key component of the towing device. During the towing, the belt is wound and unwound by means of the mobile frame and of the pulleys rotating about the object to be towed. To ensure the gripping of the object, the belt is also stressed in tension continuously. The belt, generally made of elastomer material, is exposed to the aggressivity of the marine environment, particularly in the case of a submerged towing device. For these reasons, a rapid aging of the belt has been observed. The replacement of the belt is complex and requires difficult intervention on the device.
The invention aims to mitigate these difficulties encountered by the towing devices of the prior art, by proposing a device that notably allows for increased reliability and enhanced repairability.